This invention relates to burglar protection devices or systems and, more particularly, to systems which detect an attack upon a protected structure such as safes, vaults, and the like by detecting or sensing acoustic emissions emanated during an attack.
Such systems rely upon the ability of one or more sensors to respond to the acoustic emissions produced in the course of an attack upon a structure to produce an electrical signal. The signal is operated upon and ultimately employed to provide a warning signal at one or more selected remote locations. The acoustic emissions propagate through the structure to the sensors and are generated by physical attacks upon the structure employing drills, hammers, torches, burning bars and other implements designed to force entry into the protected structure. In addition, movement of the lock mechanism or tumblers will produce such emissions. The different modes of attack on a potential structure produce different patterns of acoustic emissions. The patterns involve different amplitudes and time durations.
One difficulty encountered with the present systems of the type described is the generation of excessive false alarms. The systems require that a balance be structured between sensitivity and stability and any errors result in favor of sensitivity. With such a balance, false alarms may be triggered by "noise"; that is, emissions detected by the sensors which are of sufficient amplitude to trigger an alarm are generated by activities other than physical attack upon a protected structure.
It is desirable, therefore, to provide such a system which has an improved ability to distinguish between emissions generated by a physical attack and those generated by other sources.